Piston assembly to reduce annular pressure buildup

ABSTRACT

A system for preventing annular pressure buildup comprising: a wellbore; two or more annuli located within the wellbore; a piston assembly located adjacent to a wellhead of the wellbore; and a pipe system that connects the two or more annuli in parallel to the piston assembly, wherein when the amount of pressure in the pipe system exceeds a predetermined amount, then a piston of the piston assembly moves whereby the movement reduces the amount of pressure in the two or more annuli.

TECHNICAL FIELD

A wellbore can include multiple annuli having trapped fluids. Pressure can build up in the annuli because of heating of these fluids, which can cause damage to wellbore components if the pressure is not reduced. A piston assembly can be used to reduce the amount of pressure in the annuli.

BRIEF DESCRIPTION OF THE FIGURES

The features and advantages of certain embodiments will be more readily appreciated when considered in conjunction with the accompanying figures. The figures are not to be construed as limiting any of the preferred embodiments.

FIG. 1 is cross-sectional view of a well system showing multiple annuli and a piston assembly.

FIG. 2A is an enlarged cross-sectional view of the piston assembly prior to movement of the piston.

FIG. 2B is an enlarged cross-sectional view of the piston assembly after movement of the piston.

DETAILED DESCRIPTION

Oil and gas hydrocarbons are naturally occurring in some subterranean formations. In the oil and gas industry, a subterranean formation containing oil and/or gas is referred to as a reservoir. A reservoir can be located under land or off shore. Reservoirs are typically located in the range of a few hundred feet (shallow reservoirs) to a few tens of thousands of feet (ultra-deep reservoirs). In order to produce oil or gas, a wellbore is drilled into a reservoir or adjacent to a reservoir. The oil, gas, or water produced from a reservoir is called a reservoir fluid.

As used herein, a “fluid” is a substance having a continuous phase that tends to flow and to conform to the outline of its container when the substance is tested at a temperature of 71° F. (22° C.) and a pressure of one atmosphere “atm” (0.1 megapascals “MPa”). A fluid can be a liquid or gas.

A well can include, without limitation, an oil, gas, or water production well, or an injection well. As used herein, a “well” includes at least one wellbore. A wellbore can include vertical, inclined, and horizontal portions, and it can be straight, curved, or branched. As used herein, the term “wellbore” includes any cased, and any uncased, open-hole portion of the wellbore. A near-wellbore region is the subterranean material and rock of the subterranean formation surrounding the wellbore. As used herein, a “well” also includes the near-wellbore region. The near-wellbore region is generally considered to be the region within approximately 100 feet radially of the wellbore. As used herein, “into a well” means and includes into any portion of the well, including into the wellbore or into the near-wellbore region via the wellbore.

A portion of a wellbore can be an open hole or cased hole. In an open-hole wellbore portion, a tubing string can be placed into the wellbore. The tubing string allows fluids to be introduced into or flowed from a remote portion of the wellbore. In a cased-hole wellbore portion, a casing is placed into the wellbore that can also contain a tubing string. It is also common for more than one casing and tubing string to be installed within a wellbore. The multiple casings can be placed inside of one another and may not extend the same distance within the wellbore. A wellbore can contain an annulus. Examples of an annulus include, but are not limited to: the space between the wellbore and the outside of a tubing string in an open-hole wellbore; the space between the wellbore and the outside of a casing in a cased-hole wellbore; and the space between the inside of a casing and the outside of a tubing string in a cased-hole wellbore. When there are multiple casings and/or tubing strings, there can also be multiple annuli.

A wellbore can be separated into one or more wellbore intervals. One way to create wellbore intervals is by bringing the top of a cement column from a subsequent tubing string up inside the annulus above the previous casing shoe. However, annular pressure buildup can occur. Annular Pressure Buildup (APB) is one of many challenging issues in the oil and gas industry. APB occurs when annular fluids that are trapped between the column of cement and the surface of the land become heated due to production or higher formation temperatures. The annular fluids then expand and can exert pressure on the casing. This condition is present in all producing wells, but is most evident in deep water wells. Deep water wells are likely to be vulnerable to annular pressure buildup because of the cold temperature of the displaced fluid, in contrast to elevated temperature of the production fluid during production. This big change in temperature during production can increase the pressure in the annulus rather rapidly. Sometimes the pressure can become so great as to collapse the inner string or even rupture the outer string or casings, thereby destroying the well.

A wellhead can provide access to some or all of the wellbore annuli, and an observed pressure increase can be quickly bled off via the wellhead. However, most subsea wellhead installations do not have access to each wellbore annulus. In order to overcome the lack of access to each annulus, other attempts to solve the problem of annular pressure build up include: use of a syntactic crushable foam wrap; leaving the cement column short of previous casings; providing a leak path or bleed port; use of a compressible fluid in the inaccessible annulus; different casing designs; and full column height cementing. However, these attempts have some shortcomings, for example, cement channeling can occur due to poor mud displacement in the case of cement column short of previous casings, very high costs can be incurred in the case of enhanced casing design and full column height cementing, and a foam wrap can only be used one time to bleed off the excess pressure.

Therefore, there is a need for improved means to reduce the amount of pressure that builds up in wellbore annuli. It has been discovered that a piston assembly can be used to bleed off the excess pressure from one or more wellbore annuli. The one or more annuli can be connected via a common tubular that is connected to the piston assembly. Any excess pressure would be exerted on a piston of the piston assembly to prevent the pressure from building up within the annuli.

According to certain embodiments, a system for preventing annular pressure buildup comprises: a wellbore; two or more annuli located within the wellbore; a piston assembly located adjacent to a wellhead of the wellbore; and a pipe system that connects the two or more annuli in parallel to the piston assembly, wherein when the amount of pressure in the pipe system exceeds a predetermined amount, then a piston of the piston assembly moves whereby the movement reduces the amount of pressure in the two or more annuli.

According to other embodiments, a method of reducing the amount of pressure in two or more annuli of a wellbore comprises: connecting the two or more annuli in parallel to a piston assembly via a pipe system, wherein the piston assembly is located adjacent to a wellhead of the wellbore; and allowing a piston of the piston assembly to move when the amount of pressure in the pipe system exceeds a predetermined amount, wherein the movement reduces the amount of pressure in the two or more annuli.

Any discussion of the embodiments regarding the well system or any component related to the well system is intended to apply to all of the apparatus, system, and method embodiments.

Turning to the Figures, FIG. 1 depicts a well system 10. The well system 10 can include at least one wellbore 21. The wellbore 21 can penetrate a subterranean formation 20. The subterranean formation 20 can be a portion of a reservoir or adjacent to a reservoir. The well system 10 can be an off-shore system. The off-shore system can include, for example, an off-shore platform 100 that is located within a body of water 11. The well system 10 can include a wellhead 13 that is located on the sea floor 12. In off-shore drilling, a production tubing 22 is inserted into the body of water 11 and extends through the water to the sea floor 12 of the body of water. The sea floor 12 is the surface of the sub-water land. The body of water and the wellbore can be several hundred to several thousands of feet deep. As used herein, the term “body of water” includes, without limitation, either formed by nature or man-made, a river, a pond, a lake, a gulf, a canal, a reservoir, a retention pond, or an ocean. As used herein, the term “water” means the water located within the body of water. The water can be freshwater, salt water, effluent, produced or flowback water, or brackish water. The well system 10 can also include other components not depicted in the drawings or described herein that are commonly included in an off-shore drilling system.

The wellbore 21 can include one or more wellbore intervals. The wellbore intervals can correspond to one or more zones of the subterranean formation 20. The wellbore intervals can be formed via the use of isolation devices, for example, packers 24, cement 31, balls and seats, etc. (not shown).

The well system 10 also includes two or more annuli. The well system 10 can include two or more casing strings 23 installed within the wellbore 21. The casing strings 23, for example as depicted in FIG. 1, can be various lengths. The well system 10 can include a first annulus 25 located between the outside of the tubing string 22 and the inside of a first casing string. A second annulus 26 can be located between the outside of the first casing string and the inside of a second casing string. A third annulus 27 can be located between the outside of the second casing string and the inside of a third casing string. Of course there can be more than three annuli in the well system as well as a multitude of casing strings or tubing strings. The casing strings 23 can be partially or wholly cemented in the wellbore 21 via cement 31. Partially cemented means that the cement composition does not completely fill the annulus in which the cement is placed; whereas, wholly cemented means that the cement composition does completely fill the annulus in which the cement is placed. According to certain embodiments, at least two annuli are not completely filled with the cement 31.

Some or all of the two or more annuli (e.g., the first, second, and third annuli 25, 26, 27) can contain a wellbore fluid 32. The two or more annuli can contain the wellbore fluid 32 in addition to the cement 31. The wellbore fluid 32 can be a fluid that is introduced by an operator or a reservoir fluid. According to certain embodiments, the wellbore fluid 32 can exert a certain amount of pressure within the two or more annuli. The amount of pressure can be exerted on the outside and inside of the casing strings 23 and/or tubing string 22 making up the annuli. The amount of pressure can also increase over time. By way of example, the amount of pressure can increase due to an increase in temperature of the wellbore fluid 32 via production of a reservoir fluid or the surrounding subterranean formation temperature.

The well system 10 includes a pipe system that connects the two or more annuli in parallel to a piston assembly 200. The pipe system can include two or more pipes that are connected to a common pipe 40. The two or more pipes can correspond to the two or more annuli. According to certain embodiments, the two or more annuli are accessible from the sea floor 12 for being able to connect a pipe to the accessible annulus. By way of example, a first pipe 41 can be connected to the first annulus 25, a second pipe 42 can be connected to the second annulus 26, and a third pipe 43 can be connected to the third annulus 27. The pipes can be connected to each annulus in any manner that is known to those skilled in the art. It is to be understood that as used herein, reference to a pipe means any tubular object that allows fluids to flow through the object and does not imply a particular shape. A pipe can be any shape so long as fluids are able to flow through the pipe. The pipes of the pipe system can also be made out of a variety of materials including, but not limited to, metals, metal alloys, plastics, non-corrodible materials, etc.

The amount of pressure in each annulus of the well system can be the same or different. The initial amount of pressure from each of the pipes is the initial amount of pressure from the respective annuli that are connected to the pipes. By way of example and as depicted in FIG. 1, the initial amount of pressure in the first pipe 41 will be the amount of pressure from the first annulus 25, the initial amount of pressure in the second pipe 42 will be the amount of pressure from the second annulus 26, etc. Each of these pressures in the pipes of the pipe system will feed into the common pipe 40. By connecting the annuli with the common pipe 40, the pressure will become the same in the annuli 25, 26, 27, corresponding pipes 41, 42, 43, and the common pipe 40 of the network because of the continuity of fluids.

The well system 10 can also include one or more annuli that are inaccessible (not shown) from the sea floor. Any of the annuli can include a rupture disk 28 or other fluid flow restriction device that restricts fluid flow past the device but fails above a certain pressure rating. The rupture disk can block fluid flow past the disk when the pressure of the wellbore fluid 32 is below a certain value. Then, when the pressure equals or exceeds the certain value, the disk can rupture, thus allowing the wellbore fluid to flow out of the annulus and into an adjacent annulus. Generally, the pressure at which the disk ruptures is below the pressure at which damage to the casing strings or tubing strings forming the annulus would occur. In this manner, the strings do not become damaged by the pressure from the wellbore fluid. Preferably, any inaccessible annuli contain the rupture disk 28 or similar device. When the pressure in the inaccessible annulus equals or exceeds the pressure rating of the rupture disk, then the disk will rupture and allow the fluid within that annulus to flow into an adjacent annulus. The amount of pressure in the inaccessible annulus will then decrease as the fluid flows into the adjacent annulus. The adjacent annulus can be an accessible annulus that is connected to a pipe of the pipe system.

The common pipe 40 of the pipe system is connected to the piston assembly 200. The piston assembly 200 is located adjacent to the wellhead 13 of the wellbore. Accordingly, the piston assembly 200 can be located on the sea floor 12. Turning to FIGS. 2A and 2B, the piston assembly 200 includes a housing 201. The housing 201 can be made of a variety of materials and can be a variety of shapes. For example, the housing 201 can be made out of metals, metal alloys, plastics, non-corrodible materials, etc. The piston assembly 200 also includes a piston 202. The piston 202 can define two chambers within the housing 201. The common pipe 40 can feed into a first chamber 204 on one side of the piston 202. A second chamber 205 can be located on the other side of the piston 202 opposite of the first chamber. The second chamber 205 can be filled with a compressible gas 203 or mixtures of compressible gases. Compressibility is a measure of the relative volume change of a fluid or solid as a response to a pressure (or mean stress) change. The compressibility of a gas or mixture is dependent on the pressure, temperature, and molar volume. The compressible gas 203 or mixture can be selected from air (which generally comprises about 80% nitrogen and about 20% oxygen), oxidizer gases such as oxygen, or inert gases such as helium, and combinations thereof. Preferably the compressible gas does not include a flammable gas.

The piston 202 can move within the housing 201. Movement of the piston 202 can inversely change the dimensions of the first and second chambers 204/205. As the piston movement increases the dimensions of the first chamber 204 the dimensions of the second chamber 205 are reduced and vice versa. The compressible gas 203 within the second chamber 205 will compress as the piston moves to reduce the dimensions of the second chamber 205, for example as depicted in FIG. 2B.

When the pressure in the pipe system via the pressure from the two or more annuli increases and exceeds a predetermined amount, then the piston 202 of the piston assembly 200 moves. The pressure moves the piston 202 to reduce the dimensions of the second chamber 205 via compression of the compressible gas 203. This movement of the piston 202 reduces the amount of pressure in the common pipe 40, each of the pipes making up the pipe system, and each annulus connected to a pipe of the pipe system. In this manner, movement of the piston reduces the total amount of pressure in the two or more annuli.

The predetermined amount of pressure at which the piston 202 moves within the housing 201 can be based on anticipated conditions of the oil and gas operation. By way of example, the casing strings 23 can have a pressure rating at which above that pressure then damage could occur to the casing strings. In this example, the predetermined amount of pressure can be less than the pressure rating of the casing strings so the piston would move to reduce the pressure in the annuli prior to the casing strings becoming damaged. The predetermined amount of pressure can also be a pressure less than the amount of pressure at which wellbore components become damaged.

The amount of movement of the piston, thereby increasing the dimensions of the first chamber 204, causes a certain amount of pressure in the pipe assembly and the two or more annuli to decrease. The amount of reduction in the pressure in the two or more annuli can be calculated based on a variety of factors including, but not limited to, the temperature of the wellbore fluid 32 within the annuli, the size of the piston assembly 200 including the size of the housing 201 making up the first chamber 204 and second chamber 205, the compressibility of the compressible gas 203, and the initial amount of pressure in the two or more annuli prior to reduction.

The size of the housing 201 and the second chamber 205 can be adjusted to provide a desired pressure decrease in the two or more annuli. By way of example, the larger the dimensions of the housing 201 and second chamber 205 prior to movement of the piston 202, the greater amount of pressure decrease will occur in the two or more annuli. The type of compressible gas 203 can also be selected to provide the desired pressure decrease in the two or more annuli. According to certain embodiments, the desired pressure decrease is at least sufficient such that damage to wellbore components, such as the casing or tubing strings, does not occur. In this manner, the excess pressure within the annuli of the wellbore can be bled off into the piston assembly before any damage can occur.

After the amount of pressure in the two or more annuli is reduced or decreased, the piston 202 can move back towards the inlet into the first chamber 204. This movement decreases the dimensions of the first chamber 204 and increases the dimensions of the second chamber 205. Should the pressure in the pipe system increase again above the predetermined amount, then the piston 202 would move again to reduce the pressure in the two or more annuli.

It should be noted that the well system 10 is illustrated in the drawings and is described herein as merely one example of a wide variety of well systems in which the principles of this disclosure can be utilized. It should be clearly understood that the principles of this disclosure are not limited to any of the details of the well system 10, or components thereof, depicted in the drawings or described herein. Furthermore, the well system 10 can include other components not depicted in the drawing.

Therefore, the present system is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the principles of the present disclosure can be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is, therefore, evident that the particular illustrative embodiments disclosed above can be altered or modified and all such variations are considered within the scope and spirit of the principles of the present disclosure.

As used herein, the words “comprise,” “have,” “include,” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods also can “consist essentially of” or “consist of” the various components and steps. It should be understood that, as used herein, “first,” “second,” “third,” etc., are arbitrarily assigned and are merely intended to differentiate between two or more annuli, casing strings, wellbore intervals, etc., as the case may be, and does not indicate any particular orientation or sequence. Furthermore, it is to be understood that the mere use of the term “first” does not require that there be any “second,” and the mere use of the term “second” does not require that there be any “third,” etc. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent(s) or other documents that can be incorporated herein by reference, the definitions that are consistent with this specification should be adopted. 

What is claimed is:
 1. A well system for preventing annular pressure buildup, the system comprising: a wellbore; two or more annuli located within the wellbore; a piston assembly located adjacent to a wellhead of the wellbore; and a pipe system that connects the two or more annuli in parallel to the piston assembly, wherein when the amount of pressure in the pipe system exceeds a predetermined amount, then a piston of the piston assembly moves whereby the movement reduces the amount of pressure in the two or more annuli.
 2. The system according to claim 1, wherein the well system is an off-shore system.
 3. The system according to claim 1, wherein the wellhead is located on a sea floor.
 4. The system according to claim 1, wherein the wellbore comprises one or more wellbore intervals.
 5. The system according to claim 1, wherein at least some of the two or more annuli contain a wellbore fluid.
 6. The system according to claim 5, wherein the wellbore fluid exerts a certain amount of pressure within the two or more annuli.
 7. The system according to claim 1, wherein at least one annulus of the well system is bounded by a rupture disk or other fluid flow restriction device that restricts fluid flow past the device but fails above a certain pressure rating, and wherein at a pressure above the pressure rating any fluid within the annulus flows into an adjacent annulus.
 8. The system according to claim 7, wherein the adjacent annulus is one of the two or more annuli.
 9. The system according to claim 1, wherein the pipe system comprises two or more pipes that are connected to a common pipe.
 10. The system according to claim 9, wherein the common pipe is connected to the piston assembly.
 11. The system according to claim 10, wherein the piston defines two chambers within a housing of the piston assembly, wherein the common pipe feeds into a first chamber on one side of the piston, and wherein a second chamber is located on the other side of the piston opposite of the first chamber.
 12. The system according to claim 11, wherein the second chamber contains a compressible gas or mixtures of compressible gases.
 13. The system according to claim 12, wherein movement of the piston inversely changes the dimensions of the first and second chambers.
 14. The system according to claim 13, wherein the movement of the piston reduces the dimensions of the second chamber via compression of the compressible gas or mixtures of compressible gases.
 15. The system according to claim 1, wherein the amount of pressure in the two or more annuli is reduced to at least a sufficient pressure such that damage to wellbore components does not occur.
 16. A method of reducing the amount of pressure in two or more annuli of a wellbore, the method comprising: connecting the two or more annuli in parallel to a piston assembly via a pipe system, wherein the piston assembly is located adjacent to a wellhead of the wellbore; and allowing a piston of the piston assembly to move when the amount of pressure in the pipe system exceeds a predetermined amount, wherein the movement reduces the amount of pressure in the two or more annuli.
 17. The method according to claim 16, wherein the piston defines two chambers within a housing of the piston assembly, wherein a common pipe of the pipe system feeds into a first chamber on one side of the piston, and wherein a second chamber is located on the other side of the piston opposite of the first chamber.
 18. The method according to claim 17, wherein the second chamber contains a compressible gas or mixtures of compressible gases.
 19. The method according to claim 18, wherein movement of the piston inversely changes the dimensions of the first and second chambers.
 20. The method according to claim 19, wherein the movement of the piston reduces the dimensions of the second chamber via compression of the compressible gas or mixtures of compressible gases.
 21. The method according to claim 16, wherein the amount of pressure in the two or more annuli is reduced to at least a sufficient pressure such that damage to wellbore components does not occur. 